The present invention relates, in general, to sensors, and in particular, to a new and useful light reflectance sensor system and method.
Reflectance sensor systems have been used for many purposes, including the determination of surface measurements for conditions related to blood perfusion at depths within layered biological tissue. Reflectance sensor systems usually consist of a physical sensor and an algorithm to determine diffusion constants and other derived quantities such as oxygenation of blood. Reflectance sensor systems sample the spatial or the temporal profile of photons from light, including infrared light, returning from a diffusive medium, such as biological tissue, following their injection into the medium. The rate of change, spatially or temporally, in the number of photons exiting the medium at some distance in space/time from the source are taken as being indicative of deeper layers of tissue.
Known reflector sensor systems have implemented the use of these physical principles by algorithms that compare reflectances at two or more sites or at two or more times following the injection of photons into the tissue medium. The data at larger separations or at longer times is then taken to be indicative of the diffusion constants K at depths where readings closer to the photon source are taken into account.
Alternatives to reflectance sensor systems, for the noninvasive measurement of reflectance in biological tissue at depth, and of comparable simplicity and ease of use, are not presently available. As a result, methods that provide shallow measurements are commonly used in the clinical environment. These alternative measurement methods include transcutaneous oxygen partial pressure, photoplethysmography, pulse oximetry and laser Doppler flowmetry.
Some of the known reflectance systems and methods as well as studies relating thereto are disclosed in Muller and Ostrander, "The Effects of Absorptive Layers On Light Reflectance", Conference Proceedings, Oct. 28, 1993; Cui and Ostrander, "The Relationship of Surface Reflectance Measurements to Optical Properties of Layered Biological Media", IEEE Transactions on Biomedical Engineering, Vol. 39, No. 2, February 1992; and Cui, Ostrander and Lee., "In Vivo Reflectance of Blood and Tissue as a Function of Light Wavelength", IEEE Transactions on Biomedical Engineering, Vol. 37, No. 6, June 1990.
Typical hardware used for the known reflectance sensor systems are disclosed in U.S. Pat. No. 4,510,938; 4,380,240; 4,321,930; and 4,223,680.
Further, U.S. Pat. No. 2,358,992 is relevant for its showing of an oxygen meter using colorimetry. U.S. Pat. No. 4,796,636 is relevant for disclosing a non-invasive reflective oximeter utilizing microprocessor based signal processing.
Also, see U.S. Pat. No. 5,057,695 which is relevant for showing a technique using a difference in light reception data from a single light source to a plurality of irradiation points, based on a difference in the length of the optical diffusion paths. Also, see U.S. Pat. No. 5,218,962 which is relevant for showing a multiple region pulse oximeter probe based on difference calculations of light passing through two regions of biological tissue.
Presently, however, there is no known reflectance sensor system which extracts data from monitored reflectances in an accurate and efficient manner.